1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording by discharging ink from recording means to a recording material.
2. Related Background Art
A recording apparatus provided with the function of a printer, copying machine, facsimile or the like or a recording apparatus used as an output equipment for a complex machine or a work station including a computer, a wordprocessor, and the like, is structured to record images (including characters, symbols, and others) on a recording material (recording medium) such as a sheet or a thin plastic board (OHP or the like). Such recording apparatuses can be divided into those of an ink jet type, wire-dot type, thermosensitive type, thermal transfer type, laser beam type in accordance with to the recording system of recording means to be used.
A recording apparatus of a serial type adopts a recording method where its main scan is performed in the direction intersecting the feeding direction of a recording material (that is, the subscanning direction). In this apparatus, after a recording material is set at a predetermined recording position, images (including characters, symbols, and others) are recorded by recording means mounted on a carriage movable along the recording material (that is, the main scanning). Then after the completion of one-line portion of an image, the sheet is fed (subscanned) for a predetermined amount, thus recording the next line portion of the image (main scanning) subsequently. By repeating this operation, the image is recorded in a desired area of the recording material. On the other hand, in a recording apparatus of a line type, the recording is performed only by subscanning where the recording material is fed. In this apparatus, a recording material is set at a predetermined recording position, and then, a sheet feed is performed for a predetermined amount (that is, the pitch feeding) while the recording of a one-line portion is being made continuously altogether. In this way, the image is recorded on the entire area of the recording material.
Of these types, those of an ink jet type (ink jet recording apparatuses) record by discharging ink from recording means (recording head) onto a recording material, making it possible to provide compact recording means easily so that highly precise images can be recording at high speeds. With this type, it is also possible to record on an ordinary sheet without any particular treatments, hence lowering its running cost. Being non-impact, this type makes less noises besides a remarkable advantage that many different colors of ink can be used for recording color images without difficulty. Particularly, in a recording apparatus of a line type using a line type recording means where many numbers of discharge ports are arranged in the width direction of a sheet, it is possible to provide a higher speed recording.
Especially, recording means (recording head) of an ink jet type which discharges ink by utilizing thermal energy can be fabricated with ease to provide the one in which liquid passages (discharge ports) are arranged in a high density by the film formation of electro-thermal transducers, electrodes, walls of liquid paths, and a ceiling on a base board through etching, deposition, sputtering, and some other semiconductor fabrication processes. This makes it possible to implement manufacturing the recording means more compactly. Also, with the utilization of such known advantages of the IC technologies and micro machining techniques, it becomes easier to elongate the recording means or effectuate its surfacing (two-dimensional arrangement), and also, to make it fully multiple and highly densified when it is assembled.
In general, an ink jet recording apparatus of a serial type comprises means for recording (recording head); a carriage which travels (main scans) with the recording means mounted thereon and its driving system; a platen for holding and feeding a recording material and a feeding (sheet feed) system; and a system for recovering discharge for maintaining and recovering the ink discharge performance of the recording means.
In an ink jet recording apparatus of the kind, there may be generated ink mists formed by fine secondary ink droplets in addition to the main droplets flying to the recording material when ink droplets are discharged from each of the discharge ports for recording and others. Then these ink mists and the like, which do not reach the recording material, tend to fly and adhere to the discharge port surface of the recording means. These adhering ink droplets are combined and developed to create a "wet" on the discharge port surface. Then, when this "wet" contacts the discharge ports, the discharge direction of ink droplets (main droplets) from the discharge ports is caused to be bent, and may disturb the discharge itself eventually.
In order to prevent any defective discharges caused by a "wet" of the kind, it is practiced to provide a cleaning member (an elastic wiping member made of rubber to wipe off the wet, for example) to clean the discharge port surface, and a cap as well as a pump for the recovery system in order to suck ink from the discharge ports for cleaning off the ink which adheres to the vicinity of the discharge ports. In other words, with means for discharge recovery processes including the cleaning member, the cap, and the pump for the recovery system, it is practiced to clean and remove the adhering ink before the adhering ink droplets on the discharge port surface are caused to develop into the "wet".
However, the method to wipe off the discharge port surface by use of the cleaning member (wiping member) requires rubbing in the vicinity of the fine discharge ports. As a result, ink and dust particles are pressed into the discharge ports, hence clogging them or creating a possibility that the discharge port surface is damaged. Further, because of the cleaning operations, there may be a disadvantage that the throughput is unfavorably lowered. Also, the method to suck ink from the discharge ports by use of the cap and the pump for the recovery system may result in the disadvantage that the throughput is unfavorably lowered due to the suction recovery operations (cleaning operations) in addition to the disadvantage that the running cost becomes higher because of the wasteful ink consumption.
Therefore, it is a prerequisite to minimize the frequency of discharge recovery operations (cleaning operations). To this end, there have been many inventions proposed to reduce the frequency of cleaning operations (discharge recovery operations) by predicting the "wetting" conditions developed from the ink droplets adhering to the discharge port surface while monitoring the temperature of a recording head, the environmental temperatures, the number of recording dots, and the like.
Nevertheless, these inventions are not the ones which monitor the "wetting" conditions of the discharge port surface directly. On the other hand, the "wet" itself is easily affected by the contamination of the discharge port surface and the discharging stability of the discharge ports, making it extremely difficult to predict its conditions exactly. Inevitably, therefore, the frequency of the cleaning operations (discharge recovery operations) cannot be reduced sufficiently. It is the technical problems that must be solved in consideration of enhancing the reliability of the recording head and reducing the running cost of the apparatus.